My current server is old.. and all disks are causing heatproblems which crashes the server due to writecacheproblems and the idebus. So now i bought a new disk and will remove 4 of the 8 disks and it got me thinking.
Time to upgrade to 4.4, as in make a fresh install from scratch.

However i use the server as storage for the house and im running a webhotell for me and my closest friends.

What is the best way to do this?

Build the new computer, recreate exact same users, and add packages that was added and then simply move home from the old box to the new?

If you elect to upgrade, the only supported upgrade path is to do a binary upgrade to the next release. So you would do 4 consecutive upgrades: 4.0 -> 4.1 -> 4.2 -> 4.3 -> 4.4.

If you have no applications on the OpenBSD platform, a clean install will be easier. You would only need to recreate your userids and migrate their data, and any web applications/configurations you have.

As you have been running an unmaintained system, except for your added disks some months ago, you should be aware that:

OpenBSD 4.0 has not been supported for more than a year. No security or reliability patches of any kind have been developed for it, nor has the OpenBSD Project accepted any bug reports for it, since November 1, 2007.

If you are running an unpatched 4.0-release system, you have been running a system with an open remote attack vector. It was announced and patched the first week of March, 2007 (patch #010). If you happened to choose OpenBSD for its security features, particularly as a bastion router or firewall exposed to the Internet, you have been remiss in maintaining it. There have been 15 major security and reliability patches since support for your release was dropped. This does not include the 17 security and reliability patches developed during the life of your release, if you have not implemented them.

If you feel Fedora is a better fit, then you should use it. You should select an OS based on the best fit for its intended use. (I can't comment on it's applicability as a web server or "webhotel" as I have never used it.)